Computer Simulation of Diffusing-Wave Spectroscopy of Colloidal Dispersions and Particle Gels

A computational approach has been developed to model diffusing wave-spectroscopy (DWS) behavior in colloidal systems. This model has been applied to the study of both colloidal dispersions and particle gels. The individual particle dynamics are computed from a Brownian dynamics simulation. Subsequently, a large number of photon paths through the system are generated. These paths, in combination with the mean-square displacements of the particles obtained from the Brownian dynamics simulations, are used to calculate the temporal autocorrelation function g (1)(t). The simulations reproduce the effect of the system thickness on g (1)(t) for a stable colloidal dispersion as found experimentally, as well as the effect of the composition of a bimodal dispersion. Simulations of particle gels show how the gelation process influences the correlation function. These simulations reproduce the profound changes in the correlation function seen experimentally during the gelation process and demonstrate that such effects are primarily due to changes in the particle dynamics rather than in the large-scale topology of the developing network.